Borderline Personality Disorder is a psychiatric disorder defined, in part, by recurrent impulsive and suicidal behaviors. With a suicide rate of up to 9.5 percent, BPD is among the most lethal of psychiatric disorders, comparable to affective and schizophrenic disorders. This study is the continuation of a first prospective, multidimensional study of the clinical, psychosocial and biological risk factors for suicidal behavior in patients with BPD. Following a stress-diathesis model of suicide, we assess predicted risk factors at baseline and follow patients annually for up to ten years, assessing for suicidal behavior, psychiatric co-morbidities, substance use disorders, episodes of impulsive-aggression, psychosocial stressors, treatment effects, social and clinical outcomes. The role of central serotonergic regulation in impulsive and suicidal behavior is studied using the 5HT2A specific radioligand [F-18] altanserin and PET neuroimaging. The effects of a childhood history of abuse are assessed on suicide risk, impulsive-aggressive behavior and on measures of central serotonergic function. Stressors increasing the risk of suicidal behavior include co-morbidity with Major Depression or Substance Use Disorders, Recent Life Events, and poor social support. Personality characteristics such as impulsivity and aggression represent chronic vulnerabilities to suicidal behavior. Longitudinal follow-up of suicidal patients allows testing of predictor hypotheses concerning risk factors for suicidal behavior in BPD through the application of survival analyses. Risk factors predicting recurrence and medical lethality of attempts will allow early identification of BPD patients at highest risk for suicide and inform treatment efforts.